Linking Libraries that contain circular references in GCC

Question

I am trying to link an application with multiple static libraries in GCC.

There are two libraries that cause problems. Libsupport provides a terminal for the application. It relies on libcpu to provide a serial link, timing and syncronisation. Libcpu relies on libsupport to provide queueing for serial data and more.

If I specify libsupport first when linking libcpu cannot be linked with the queue functions. Is I specify libcpu first lib support can not link the serial link (and more) functions.

It looks like GCC parses a library only once and discard any unused objects.

Can I ask gcc to parse libraries multiple times or to include all objects?

Paco

Answer 1

gcc ... -lsupport -lcpu -lsupport -lcpu

-> Each mention of a library will cause resolution of libraries that came before it (but not necessarily ones specified afterwards), which is why you may need to specify more "-lsupport -lcpu" in future.

Alternatively, try --start-group -lsupport -lcpu --end-group once.

Squiffy

The group specifier is interesting.. never seen it before. – Ligure

Answer 2

Here is detailed explanation of why either repeating libraries or using --start/--end-group is required in this situation.

Opportunist

Answer 3

You can normally specify a library more than once to get around this kind of problem, e.g.

$ gcc ... -lsupport -lcpu -lsupport ...

Peracid

I tried it but it did not work. Then I tried "-lsupport -lcpu -lsupport -lcpu" and it worked. Not sure what is happing but the application is linking. – Paco

Answer 4

Note that --start-group /  --end-group are linker options which are unknown to the compiler, so if you use gcc / g++ for linking, you should specify them as:

gcc ... -Wl,--start-group -lsupport -lcpu -Wl,--end-group

Otherwise you will get:

gcc.exe: error: unrecognized command-line option '--start-group'

gcc.exe: error: unrecognized command-line option '--end-group'

Ragsdale